Neuroendocrine Control of Energy Balance and Insulin Sensitivity In response to input from hormones such as insulin and leptin, which circulate in proportion to body fat mass, hypothalamic neuronal systems adjust feeding behavior and autonomic outflow in ways that promote homeostasis of both energy stores and fuel metabolism. Recent work from our program and elsewhere has established the hypothalamic arcuate nucleus (ARC) as a key brain area involved in both processes and identified neuronal signal transduction via the insulin receptor substrate - phosphatidylinositol-3-OH kinase (IRS-PI3K) pathway as a pivotal mediator of the actions of both insulin and leptin in this brain area. A key, unanswered question is whether signaling downstream of PI3K involving mammalian target of rapamycin (mTOR), atypical protein kinase C (aPKC) isoforms, or both pathways mediate the effects of adiposity- related hormones on energy balance and glucose metabolism;and whether signaling via these pathways is disrupted in common forms of obesity. The overarching aims of this proposal are therefore 1) to clarify the role of the ARC in comparison to other leptin-sensitive brain areas as a mediator of leptin action in the control of glucose homeostasis;2) to determine the roles played in the ARC by mTOR and aPKCs as mediators of neuronal signal transduction downstream of PI3K in the action of leptin on glucose metabolism;and 3) to determine whether dysfunction within either or both of these signal transduction pathways contribute to the effect of diet-induced obesity (DIO) on glucose metabolism. To accomplish these goals, we will employ state-of-the-art histochemical, biochemical, physiological and gene therapy techniques in both normal rats and in genetically obese, insulin-resistant Koletsky (fak/fak) rats that lack all leptin receptor to investigate whether disorders of this control system cause both weight gain and insulin resistance, cardinal features that link obesity with type 2 diabetes.